The invention relates generally to semiconductor device fabrication and, in particular, to parameter extraction for device models.
Device models are commonly used to scientifically model the physical phenomena observed during the operation of semiconductor devices, such as complementary metal oxide semiconductor (CMOS) devices like field effect transistors. Physically-based device modeling for the operational description of semiconductor devices is essential during the design phase to ensure the reliability of integrated circuits containing the semiconductor devices. The device model is an input for a circuit simulator.
Semiconductor manufacturing technologies generally consist of a group of different transistor types to facilitate many types of circuit designs. Compact models are created for each of these transistor types. Because many of the processing steps are shared among different devices, different devices can often have similar characteristics. However, because compact model extraction is done on a device-by-device basis, these similarities can be lost in the model. This is generally more apparent where the device model has to be extrapolated into a space where no hardware data exists.
Some devices may be categorized into device families, sharing many device characteristic but different in certain other characteristics (e.g., high VT, low VT). These devices have characteristics that are similar in a lot of ways and should behave similarly as well. A single device model may have several hundred parameters to fit. Some parameters shared by these devices should have relationships and some should not. Contemporary modeling tools generally address one device at a time. When device modelers extract a device model for a device with a high VT, for example, they may fit the device model to achieve better correlation to data physically obtained from the device. Other device modelers may encounter a device model for a similar device with a low VT and fit the parameters for this model differently, where if they were evaluated together, might result in a simple scaling of some parameters of the device model. Because different individuals may be extracting device models and because the extractions for the device models of families of devices may be done at different times, inconsistencies may be introduced into the models that are not discovered until quality checking is performed. Additionally, contemporary model extraction tools do not force any consistency between related devices. Consistency is generally checked at the end of the modeling process and if problems exist, they are typically corrected by adjusting parameters and reextraction, forcing repetition of steps in the process and adding time to the overall design.
What is needed therefore is a methodology to provide better consistency between models and model parameters.